1. Field of the Invention
The present invention relates to a high-frequency module that enables a plurality of communication signals having different frequency bands to be transmitted and received using a common antenna.
2. Description of the Related Art
Currently, a wireless communication device such as a cellular phone is required to be capable of transmitting and receiving communication signals of a plurality of types with diversification and multichannel of communication specifications. In this case, an antenna that is common to the plurality of types of communication signals is used for reducing the wireless communication device in size and so on.
When the common antenna is used, a first transmission/reception circuit transmitting and receiving a first communication signal and a second transmission/reception circuit transmitting and receiving a second communication signal are connected to the common antenna. That is to say, one end of the first transmission/reception circuit and one end of the second transmission/reception circuit are connected with a connection point to the common antenna interposed therebetween.
For example, a multiband duplexer module as disclosed in Japanese Unexamined Patent Application Publication No. 2010-45563 includes a common antenna terminal, a first duplexer (first transmission/reception circuit), and a second duplexer (second transmission/reception circuit). In the multiband duplexer module, one end of the first duplexer and one end of the second duplexer are connected and a connection point thereof is connected to the common antenna terminal.
In the high-frequency module (multiband duplexer module) as disclosed in Japanese Unexamined Patent Application Publication No. 2010-45563, an impedance matching circuit is connected between the first duplexer and the connection point of the first duplexer and the second duplexer. The impedance matching circuit performs impedance matching between the first duplexer and the common antenna terminal.
However, the high-frequency module as disclosed in Japanese Unexamined Patent Application Publication No. 2010-45563 causes the following problems.
Currently, a frequency band of a channel of each communication signal is required to be broadened in order to increase communication speed. A frequency bandwidth available for a single communication band is, however, limited. Accordingly, it has been proposed that the communication channel is substantially broadened by using a plurality of communication bands simultaneously. This method is called carrier aggregation (CA).
When the CA is applied to the above-mentioned high-frequency module, the high-frequency module transmits and receives a first communication signal using a first frequency band with the first duplexer and transmits and receives a second communication signal using a second frequency band with the second duplexer simultaneously. It should be noted that in this case, the high-frequency module transmits and receives both the first and second communication signals in some cases and the high-frequency module transmits and receives only one of the first and second communication signals in other cases.
In the configuration in which the first transmission/reception circuit and the second transmission/reception circuit are connected to the common antenna or the common terminal, when a harmonic frequency of a transmission signal (first transmission signal) of the first communication signal is close to a fundamental frequency of a reception signal (second reception signal) of the second communication signal or at least a part of the harmonic frequency of the transmission signal (first transmission signal) overlaps with the fundamental frequency of the reception signal (second reception signal), the harmonic signal of the first transmission signal leaks to the second duplexer. Due to this leakage, reception sensitivity to the second reception signal is deteriorated.